Attaching a Ball Grid Array (xe2x80x9cBGAxe2x80x9d) Zero Insertion Force (xe2x80x9cZIFxe2x80x9d) socket onto a rigid FR-4 header with press fit pins inserted into it and then attaching that assembly to a flexible circuit using solder preforms is one previous way of providing for a Flex-Rigid-Flex probe with pins.
Another way to provide a Flex-Rigid-Flex probe with pins is to laminate a rigid PC Board to a flexible circuit board and then attach solder balls to either side of the rigid-flex laminate. A socket is then soldered to one side and a PGA header is soldered to the other side of the laminate assembly.
Both of the prior art methods of providing a Flex-Rigid-Flex interposing probe with pins unduly lengthen the bus. Further, construction of the interposing probes utilizing the above mentioned methods results in multiple reflow cycles thus increasing the likelihood of re-reflowing solder connections and creating shorts in the BGA field.
The present invention provides a method for constructing a Flex-Rigid-Flex interposing probe with pins. The method of the invention allows for reduced bus lengthening by an interposing probe and increases the electrical invisibility of the probe to the target system. Further, the method of the invention integrates the assembly of the Pin Grid Array (xe2x80x9cPGAxe2x80x9d) socket or header with the flexible attachment into a single process containing only one reflow cycle. Still further, the single reflow cycle applies to only one side of the flexible attachment. Still further, the method of the invention provides that SMT components near the pins in the interposing probe be soldered onto the rigid PC board as opposed to the flexible attachment. This increases the durability and reliability of the solder joints in the affected area of the probe.
The method of the invention provides a single step process for solder attaching PGA pins to a BGA header. Also, the method of the invention requires a reduced number of components. As discussed, the durability and reliability of SMT solder joints and BGA solder joints are increased.
The method of the invention also provides for ease in manufacturing a Flex-Rigid probe. The BGA socket can be soldered onto the flexible attachment at the same time as the pins and SMT components are soldered. One reflow cycle reduces the chances of re-reflowing solder balls and creating shorts in the BGA field.
The method of the invention comprises the step of first creating the lay out of the flexible attachment. Top and bottom rigid PC Boards are lain out and drilled. The drill creates holes that are the press fit diameter of nail. The holes are then plated with an annular ring on the outer exposed surface. The next step comprises laminating the flexible circuit between the two rigid PC Boards. Press fit nail pins are inserted through the holds in one side of the laminate sandwich until flush with the surface of the PC Board. Solder preforms are soldered the bottom surface of the laminate sandwich. The preforms mechanically and electrically attach the pins to the bottom rigid PC Board. A BGA socket can then be attached to the pins extending from the bottom of the laminated Flex-Rigid-Flex assembly.